1. Field of the Invention
The present invention relates to improvements in a floating-type core slider of a magnetic head for a rigid magnetic disk drive.
2. Discussion of the Prior Art
In the art of a rigid magnetic disk drive (sometimes abbreviated as "RDD"), there is known a floating-type magnetic head which employs a bulk type core slider, such as a monolithic type slider as indicated generally at 1 in FIG. 1. This core slider 1 is an integral structure consisting of a slider body 2, and a yoke portion 3 which is generally C-shaped in cross section. On one surface of the slider body 2 on which a recording medium in the form of a magnetic disk slidably rotates, there are formed a pair of parallel spaced-apart air bearing portions 4a, 4b which extend in the rotating or sliding direction of the magnetic disk. The sliding surfaces of the air bearing portions 4a, 4b have a suitable height as measured from a recessed portion therebetween. The core slider 1 has a center rail 5 which is formed between the air bearing portions 4a, 4b so as to extend parallel to the air bearing portions. The center rail 5 serves as a track portion whose surface has the same height as the air bearing portions 4a, 4b. In operation, the selected recording track of the magnetic disk is aligned with the track portion or center rail 5. The yoke portion 3 indicated above is formed integrally with the slider body 2, at one of opposite ends of the center rail 5. The yoke portion 3 and the slider body 2 cooperate with each other to define a closed magnetic path for the magnetic head.
The monolithic type core slider 1 formed solely of a ferrite material is rlatively economical to manufacture. The width of the elongate track portion is determined by tapering or chamfering the parallel edges of the center rail 5. This manner of forming the track portion suffers from difficulties in precisely establishing the desired track width, and in reducing the track width. Further, when the core slider 1 is moved off the surface of the magnetic disk, both air bearing portions 4a, 4b should lie within the range of radius of the magnetic disk. Namely, the center rail or track portion 5 located between the two air bearing portions 4a, 4b should be positioned a given distance away from the outer periphery of the magnetic disk in the radially inward direction. Therefore, the effective recording surface area of the magnetic disk is reduced to an extent corresponding to the distance between the track portion 5 and the air bearing portion 4a, 4b. In other words, the data storage capacity of the magnetic disk is limited by the construction of the core slider 1.
There is also known a composite type core slider which is produced by a slider body and a head core which are separately prepared. More specifically, a ferrite core having a track portion formed perpendicularly to a surface thereof is partially embedded in and fixed to a non-magnetic slider body. This composite type core slider is advantageous over the monolithic type, in that the track portion can be formed with its width accurately controlled to a desired value, and that the width can be made relatively small. The composite type is further advantageous in that the track portion can be formed in alignment with an air bearing portion, i.e., formed on a line of extension of the air bearing portion, whereby the outer peripheral portion of the magnetic disk can be used as an effective recording area. However, the composite type core slider is disadvantageous in the cost of manufacture, because of the steps of separately preparing the slider body and the core, and then joining these two members together.
A further type of core slider is proposed according to laid-open Publication No. 62-18615 of unexamined Japanese patent application, in an attempt to lower the cost of manufacture while enjoying the functional advantages of the composite type discussed above. In this proposed core slider, a yoke portion is formed integrally with a slider body, at one end of an air bearing portion formed on the slider body, such that the yoke portion and the slider body cooperate to constitute a head core which has a magnetic gap. To produce this core slider, grooves defining a track portion are formed in appropriate two blocks, and the two blocks with the grooves filled with a glass material are butted together and bonded by the glass material, such that selected parts of the joining surfaces define the magnetic gap therebetween. Subsequently, the obtained body of the bonded blocks is subjected to a grooving operation to form the air bearing portion and the yoke portion.
In the core slider of the type described above, the track portion is in line with the air bearing portion, and therefore these two portions may be concurrently formed by the grooving operation, contrary to the air bearing and track portions of the monolithic type core slider which are spaced apart from each other. However, this type of core slider requires the step of establishing the desired width of the track portion by the grooving operation, and an additional step of filling the grooves with the glass material, and consequently suffers from a relatively increased total number of process steps, which counterbalances the advantage of the concurrent formation of the track and air bearing portions. In addition, the cross sectional area of the yoke portion of the core slider in question tends to be larger than that of the composite type core slider and the monolithic type core slider of FIG. 1. This results in an increase in the inductance of the head core, which is disadvantageous in performing high-frequency recording operations on the magnetic disk. That is, the core slider is not capable of assuring sufficiently high density of recording per unit area of the magnetic disk.
For producing the conventional core slider as shown in FIG. 1 wherein two spaced-apart air bearing portions and a center rail are provided, the grooving operations to form the air bearing portions and center rail and the chamfering operations to determine the width and length of the formed bearing portions and rail are performed by using a grinding wheel such as a diamond wheel. The grooving and chamfering operations require a total of eight grinding passes for each core slider, and are the most time-consuming steps of the process. Further, the error in the widths of the air bearing portions and track portion (center rail) cannot be held within a permissible range of .+-.3 microns, due to unavoidable positioning error of the grinding wheel, and due to inevitable variations in the thickness or height of the blank for the slider body and positioning error of the yoke portion bonded to the slider body blank. Moreover, the surfaces finished by the diamond wheel inevitably suffer from chipping of one micron or more.